The invention relates to the severing apparatus in general, and more particularly to improvements in apparatus for repeatedly severing a running web of plastic, paper or other flexible material so that the web yields a series of discrete web sections. Apparatus to which the invention pertains can be utilized with advantage in filter tipping machines of the tobacco processing industry, namely in machines wherein sections of filter rods are united with plain cigarettes, cigarillos or cigars to form filter cigarettes, cigarillos or cigars of unit length or multiple unit length.
A filter tipping machine comprises means for assembling sections of filter rods with sections of tobacco containing rods (such as plain cigarettes) so that the sections form groups of coaxial rod-shaped articles. The machine further comprises a source of convoluted web of tipping paper, a paster which applies adhesive to one side of the web, an apparatus which subdivides the web into a series of so-called uniting bands, and a mechanism which drapes the uniting bands around successive groups of coaxial articles to thus convert the groups into filter cigarettes, cigars or cigarillos of unit length or multiple unit length.
As a rule, the web severing apparatus employs a drum-shaped counterknife and a rotary carrier for one or more knives which cooperate with the counterknife to sever the leader of the web in the space between the periphery of the counterknife and the path of orbital movement of the cutting edge or edges of one or more knives. A certain length of the leader of the web is attracted to the periphery of the counterknife by suction. Successively severed uniting bands are caused to adhere to successive groups of coaxial rod-shaped articles to be convoluted around the planes of abutment between the end faces of filter rod sections and the adjacent end faces of plain cigars, cigarillos or cigarettes.
The cutting edge of each knife on the rotary knife carrier extends transversely of the path of forward movement of the web with the periphery of the counterknife. Reference may be had to commonly owned U.S. Pat. No. 4,485,710 to Schlisio et al. The cutting edge of each knife strikes against the exposed surface of the leader of the web once during each revolution of the knife carrier to thus penetrate through the web and separate a uniting band therefrom. In other words, the cutting edge of each knife actually strikes against the peripheral surface of the counterknife once during each revolution of the knife carrier. Each cutting edge severs the web all the way from one marginal portion to the other marginal portion in a single step, i.e., any portion of a cutting edge penetrates through the web and contacts the peripheral surface of the counterknife simultaneously with each other portion of the same cutting edge. This is a so-called crush cutting operation.
In order to ensure that the web will be cut all the way from the one to the other marginal portion, the cutting edge of each knife must strike the web, and immediately thereafter the peripheral surface of the counterknife, with a considerable force with attendant generation of pronounced noise.
British Pat. No. 2,123,737 discloses a modified web severing apparatus wherein the counterknife carries a set of knives which are inclined with reference to the axis of the counterknife. Such knives cooperate with the knives of the knife carrier on which the knives are mounted in exact parallelism with the axis of rotation of the carrier. The arrangement is such that successive knives on the knife carrier cooperate with successive knives of the counterknife in order to ensure that the cooperating cutting edges of the knives are in a mere point contact with each other and the point of contact travels from one marginal portion toward the other marginal portion of the web. This contributes to a reduction of noise but such apparatus exhibits a number of other drawbacks, especially as concerns the cost of making, assembling and adjustment.
The British patent further discloses the advisability of reducing the speed of forward movement of the web immediately after the making of each cut to thus establish a clearance or gap between the trailing end of the freshly severed uniting band and the front edge of the freshly formed leader of the web. The establishment of such gaps is desirable in connection with further processing of successively formed uniting bands. The means for changing the speed of the web in order to ensure the establishment of gaps comprises a roller which is mounted on a lever having a follower which tracks a cam. The roller alternately shortens and lengthens the path of movement of the web on its way toward the counterknife to thus accelerate and decelerate the web in synchronism with angular movements of the counterknife. A drawback of this proposal is that the roller causes vibratory stray movements with attendant agitation of the web ahead of the counterknife and the making of unsatisfactory cuts. Stray movements are likely to develop when the web is advanced at a relatively high speed which is necessary in a modern filter tipping machine.